Aviation fuel



' scribed in Patented Feb. 16; 1943 I UNITED STATES PATENT, OFFICE AVIATION FUEL Alexis Voorhies, In, Baton Rouge, La., assignor,

by means ass No Drawing.

9 Claims.

This invention relates to aviation fuel and is more particularly concerned with a method of preparing an aviation fuel rich in aromatics having a high octane number and a high net heating value.

Recently there has been a substantial increase in the demand for aviation fuels of octane numbore in excess of 90 by ,the A. S. T. M. method and of '92 or more by the Army method. In addition to the requirement that the octane number must be a certain minimum it is also specified, among other things, that the lower or net heating value of the fuel shall be at least 18,500 B. t. u. per pound.

The lower or net heating value is determined by the following formula:

H-wx 1050 where H is the higher or gross heating value of the fuel in B. t. u. per pound, and w is the weight in pounds of water per pound of fueL The higher or gross heating value is determined in accordance with A. S. T. M. method D-240-2'7. The weight in pounds of water per pound of fuel is determined in accordance with the method de- Determination of Carbon and Hyignments, to Standard Catalytic Company, a corporation of Delaware Application September 16, 1939, Serial No. 295,257

otherwise chemically reconstructed product, for

' example of anti-knock characteristics superior to those of the starting material, with or without an accompanying change in molecular weight. By the term chemically reconstructed is meant something more than the mere removal of impurities or ordinary finishing treatments. The term catalytic reforming shall be understood to include, but not by way of limitation, reactions such as dehydrogenation, aromatization or cyclization, desulfurization, alkylation and isomeriza tion. all or some of which may occur to a greater or lesser extent during the process.

It is observed that in catalytic reforming in the presence of hydrogen there is a substantial formation of aromatic hydrocarbons. While these aromatics are characterized by high octane numdrogen in Gasoline and other Volatile Liquids,

Industrial and Engineering Chemistry (analytical edition), volume 9, No. 7, July 15, 1937.

I have found that an aviation gasoline should have a hydrogen content of at least 13.5% in order that the lower heating value will be at least 18,500 E. t. u. per pound. I have also found that many processes by which aviation gasolines of the required octane number can be prepared produce gasolines in which the hydrogen content is appreciably below 13.5% and consequently the lower heating value is below the required minimum of 18,500 B. t. u. per pound.

One particularly suitable method for preparing aviation gasolines of high octane number is a process of catalytic reforming in the presence of substantial quantities of added hydrogen carried out under such conditions of time, temperature, pressure and feedrate that there is a substantial net production of free hydrogen in the process.

The term catalytic reforming wherever used in the specification and claims shall be understood to mean any process of subjecting materials consisting essentially of hydrocarbons substantially boiling in the gasoline range to heat treatment at a temperature inexcess of 500 F. and in the presher and have other characteristics which make them desirable for use in aviation fuel, they are also characterized by low hydrogen content which is unfavorable from the standpoint of high net heat of combustion. The problem therefore is to ilnd some way to take advantage of the desirable characteristics of aromatic hydrocarbons and to offset their deficiency in hydrogen,

The present invention therefore has for its principal object the provision of a process by which an aromatic aviation fuel ofhigh octane number and high net heating value may be produced. The nature of the process and the manner in which it is carried out will be fully understood from the following description.

A hydrocarbon oil of relatively low octane number and having a boiling range between say l00 and 500 F. is subjected to catalytic reforming in the presence of hydrogen. The hydrocarbon oil may be derived from any source and it is immaterial whether it is parafiinic, naphthenic, aromatic,

cleflnic or contains high or low sulfur content. The oil, preferably in admixture with hydrogen or a gas-rich in free hydrogen, is heated to a temperature between 850 and 1050 F. under a pressure between atmospheric and 500 lbs. per square catalysts may contain from 1 to 50% or more of the active metal oxide, and may be prepared in several different ways, i. e. by mechanical mixing of the ingredients, by impregnating the aluminum oxide with a solution of the metal salt and then heating to convert the metal salt to the oxide, or by co-precipitating aluminum hydroxide and the hydroxide of the active metal from a solution containing soluble salts of the two.

The quantity of gas containing hydrogen which is passed with the oil over the catalyst is preferably between 1000 and 4000 cubic feet per barrel of oil and this gas should contain from 20 to 90 mol per cent of free hydrogen. The rateat which the oil is passed over the catalyst is preferably between 0.3 and 3.0 volumes of liquid oil per volume of catalyst per hour..

The passage of oil andhydrogen over the cataiyst is continued until 1) the octane number of the liquid product produced, as indicated by the aniline point thereof, falls below the desired level or (2) there ceases to be a net production of free hydrogen in the reaction, whichever of these things occurs first. With most of the catalysts mentioned above, this time may vary from 3 to 6 hours'or more. At the end of this time or cycle. it is necessary to regenerate the activity of the catalyst and the manner in which this can be done will be explained below.

The products leaving the reaction'zone which consist of hydrocarbon vapors and hydrogen are passed through a cooler, and then into .a separator wherein liquid and gaseous products are separated. v

The gaseous products which contain substantial quantities offree hydrogen are removed and may be recycled directly to the reaction zone to provide the gas rich in free hydrogen required therein. or a portion or all of them may first be scrubbed with oil or otherwise treated to remove some of the hydrocarbon constituents and thereby increase the concentration of hydrogen therein. It will be understood that once the process has started up 'it will not be necessary to add hydrogen from an extraneous source because the hydrogen produced in the process is sufficient to maintain the required concentration in the recycle gases.

The liquid products are removed from the separator, pressure is released thereon whereby further quantities of gas are evolved, and these gases are removed from the system. The products whiehstill remain liquid are passed into a fractionatlng and stabilizing tower and a fraction boiling in the aviation fuel range is separated .thcrefromf. This product will have a substanthereon are removed by combustion. The quantity of gases passed through the catalyst may vary from 1000 to 3000 volumes of gas per volume of catalyst per' hour. The gases are heated to a temperature of 600 to 900 F. and care should be taken that the highest temperature in the reaction zone does not exceed about 1200 F. One method of temperature control is through the oxygen concentration of the regeneration gases. For example, at the start of the regeneration when combustion is rapid the concentration of oxygen may be low such as 0.3% and as the regeneration proceeds the quantity may be increased to 10 or even 21%.

The flow of regenerating gases is ordinarily continued until there is no longer a consumption of oxygen therefrom. This will indicate that no further combustible material remains on the catalyst. After regeneration the catalyst may be used again in a reaction cycle and alternate reaction and regeneration cycles may be carried out an indefinite number of times.

Following fractionation and if necessary rerunning, the 1 product of the above process is blended with a sufficient quantity of a hydrocarbon having an octane number at least as high as that of the product and a hydrogen content substantially above 13.5% to bring the hydrogen content .of the entire mixture up to or above 13.5%. are isopentane and isobutafie or isopentane which have been alkylated with normally gaseous oleflns. These hydrocarbons may be obtained from any source. An especially convenient source of isopentane is the feed stock itself which may be depentanized prior to the catalytic reforming treatment, and the pentane so obtained isomerized in any known manner, such as by heating in the presence of aluminum chloride and hydrogen chloride. Part or all of the isopentane so obtained may be blended with the reformed product. It will be understood of course that the quantity of isopentane added should not be willcient to make the final blend too volatile.

tially higher octane number than the feed stock.

and, unless the conditions of operation have been 50 selected and held within such narrow limits as to retard the formation of aromatics, will be substantially richer in aromatic hydrocarbons than the feed stock. In most cases, the aromatic content of' this product will range between 20 and 55%.. However, in such cases, the hydrogen content will be appreciably below the 13.5% minimum necessary to insure a lower net heating value of at least 18,500 B. t. u. per pound.

Returning to the regeneration referred to above, when the catalyst requires regeneration the flow of oil and hydrogen is stopped, the reaction chamber is purged of oil by passing inert gases or steam therethrough and then hot inert gases containing regulated quantities of air or oxygen are passed over the catalyst whereby the coke and carbonaceous contaminants deposited The quantity of isopentane that must be added will naturally depend upon the hydrogen content of the reformed fuel and the volatility desired in the final fuel. In general I have found that quantities of isopentane between 5 and 15% may be used with satisfactory results.

The following examples illustrate how the invention is applied:

Erample 1 A light naphtha derived from an East Texas crude and having the following characteristics:

Gravity; A. P. I 83.3 Aniline point, F 131 Octane number, A. S. '1. M 59.2 Bromine number 1 Initial boiling point, F 117 Final boiling point, F 845 Percent aromatics 15 is subjected to catalytic reforming in the presence of hydrogen under the following conditions:

Catalyst Activated alumina an molybdenum oxide Length of cycle, hours 6 Suitable hydrocarbons for. this purpose to at least 18,500 B.

It will also be understood that this method is v A gasoline boiling in the aviation fuel range is separated from the product of this treatment and treated with #/bbl. of 98% sulfuric acid. This treated gasoline has the following char acteristics: Gravity, A. P. I 55.3 Aniline point, F 62 Octane number, A. 8. T. M. 79.6 +3 cc. lead 90.5 +6 cc. lead 93.6 Bromine number a 8 Army ,mgs 1.4 Acid heat, F. A. S. T. M 11 Reid V. P., lbs./sq. in 5.9 Initial boiling point, "F 127 Per cent 167 F 22.0 Per cent 212 "F 52.0 Per cent 293 F 98.0 Final boiling point, F 319 Yield on feed, vol. per cent '19 Gross heat of combustion. B. t. u./1b 19548 Net heat of combustion, B. t. u./lb 18333 Hydrogen content, per cent 12.8 Per cent aromatics 42 20% and 30% respectively of an alkylate prepared by alkylatingisobutane with butylenes is added to the above fuel and the characteristics of the blend are then as follows:

Aikylate Added Gravity A. P. I OetancnumberA.S.T.M. +3 co.

+0 cc. les. :11. Initial boiling point It will be seen from the above example that the net heat of combustion can be increased from 18,333 to at least 18,500 B. t. u./lb. with an actual increase in the octane number.

Ezamplez To another portion of the same acid-treated hydroformed naphtha is added 11% of isopentane and it then has the following characteristics:

Gravi y -A. P. I 58.4 Gros' heat of combustion, B. t. u./lb 19,720 Net heat of combustion, B. t. u./lb 18,462 Hydrogen content, per cent 13.3

' It will be seen from the above example that the addition of about 15% of isopentane to the base stock will increase the net heat of combustion t. u./lb.

While the above description of the invention has been made with particular reference to an aviation fuel prepared by a process of catalytic reforming in the presence of hydrogen, it will be understood that the method of increasing the net heat of combustion to at least 18,500

B. t. u./lb. is equally applicable to aviation fuels,

prepared by other processes, such as catalytic cracking, catalytic reforming, thermal cracking, thermal reforming and the like.

Per cent hydrogen 1 Lower net heating by weight value B. t. 11. per pound These figures when plotted fall on a straight line so that intermediate values may be readily determined. In using such a plot due allowance should of course be made for experimental deviations from the curve.

This invention is not limited by any theories of the mechanism of the reactions nor by any details which have been given merely for purposes of illustration but is limited only in and by the following claims in which it is intended to claim all novelty inherent in the invention.

I claim:

1. The method of increasing the net heat of combustion of an aviation fuel containing between 20 and 55% of aromatic hydrocarbons to at least 18,500 B. t. u. per pound without substantially affecting the octane number of said fuel which comprises adding thereto a sufficient quantity of a hydrocarbon having an octane number at least equal to that of the fuel and a hydrogen content in excess of 13.5% to bring the hydrogen content of the mixture to at least 13.5%.

2. Method according to claim 1 in which the hydrocarbon added to the fuel is isopentane.

3. Method according to claim 1 in which the hydrocarbon added to the fuel is an alkylate of isobutane and a normally gasecus'olefin.

4. Method according to claim 1 in which the hydrocarbon added to the fuel is an allwlate of isopentane and a normally gaseous olefin.

5. The method of preparing an aviation fuel having an A. S. T. M. octane number with 3 cos. of tetraethyl lead in excess of and a net heat of combustion of at least 18,500 B. t. u. per pound which comprises adding to a hydrocarbon oil containing between 20 and 55% of aromatic hydrocarbon, consisting essentially of hydrocarbons boiling in the aviation fuel range and prepared by a process of catalytic reforming in the presence of hydrogen carried out under such conditions that there is a net production of free hydrogen in the reaction, a minor quantity of a hydrocarbon having an octane number at least equal to that of said hydrocarbon oil and a hydrogen content in excess of 13.5% by weight suflicient to bring the hydrogen content of the mixture to at least 13.5% by weight.

6. Method according to claim 5 in which the hydrocarbon added is isopentane.

the hydrogen content should 1 A. Method according to claim 5 in. whlch the 9. Method according to c1a1m'5 in which an 'frowrbon. added is an alk'ylate o1 isopentane hydrocarbcn added is isopentane and the qugu- 1 a tltylthereof added is between 5 and 15%; by

* volume.

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